This invention relates to an adjustable alignment assembly for the cryogen venting system for a superconducting magnet, particularly suitable for connecting the cryostat vent to the atmospheric vent in the room in which the superconducting magnet is installed.
As is well known, a magnet can be made superconductive by placing it in an extremely cold environment, such as by enclosing it in a cryostat or pressure vessel containing liquid helium or other cryogen. The extreme cold reduces the resistance in the magnet coils to negligible levels, such that when a power source is initially connected to the coil (for a period, for example, of ten minutes) to introduce a current flow through the coils, the current will continue to flow through the coils due to the negligible resistance even after power is removed, thereby maintaining a magnetic field. Superconducting magnets find wide application, for example, in the field of magnetic resonance imaging (hereinafter "MRI").
MRI systems and equipment are typically installed in specially designed hospital rooms or units which include appropriate shielding and isolation from extraneous magnetic fields and a vent to the atmosphere, generally through the ceiling of the room, all of which are designed and usually prepared in advance of the delivery and installation of the MRI. When the MRI is positioned and installed at the user or customer site, the vent adapter on the MRI must be connected by piping to the previously installed piping in the ceiling of the installation. This enables the helium gas resulting from the boil-off of the liquid helium to be vented through the ceiling of the building or hospital in which the MRI is installed to the atmosphere outside the building.
Careful consideration must be directed not only to conducting the normal boil-off of helium gas to the atmosphere which under normal operating conditions is a very low flow such as in the order of 0.2 liters per hour, but also to the extremely heavy helium gas flow of up to 9000 grams per second, and high pressures in the order of 35-40 pounds per square inch gauge (psig) which occurs if the superconducting magnet should quench or revert to a non-superconducting state. It is important that the venting system safely carry off the helium gas vapor under both conditions, without allowing any significant leak of helium gas into the MRI imaging room or rupture of the venting system in the event of a magnet quench.
Notwithstanding careful and precise dimensioning and design in advance of installation, the magnet vent adapter frequently does not precisely line up with the ceiling vent pipe which is already installed and cannot be moved. This results because the precise location of the superconducting magnet in the MRI imaging room is predetermined by the location of the magnet mounting bolts that have already been set in place by the building contractor. Thus, the need arises for a vent pipe interconnecting system which is capable of compensating for the final small vent system misalignment which is generally in the order of less than one inch of variation in any radial direction.
The use of flexible piping such as stainless steel "corrugated" piping somewhat similar in appearance to that used to connect dryers in a home to a vent, has proven difficult to use since the stainless steel, even with corrugations, is not really flexible over the short length often required. Flexible alternative materials do not have sufficient strength or cryogenic resiliency in the event of a superconducting magnet quench.
It is thus highly desirable that the vent interconnecting system provide lateral movement between the building vent pipe and the MRI vent adapter.
However, it is necessary that the adjustable vent piping be gas-tight, and suitable for carrying cryogen boil-off even in the event of quenching of the magnet, in which as much as 1800 liters of helium may be boiled off in a matter of only 20 seconds, producing tremendous volumes and pressures of cryogenic temperature cryogen gas.